Substituted 1,2,4-triazolo[1,5-a]pyrimidine-2-sulfonanilides (I) ##STR1## are valuable herbicides for the selective control of weeds in agronomic crops. Among the more valuable herbicides of formula (I) are those described in U.S. Pat. No. 4,818,273 in which the substituents A are both either halo, hydroxy or alkoxy. Compounds of this family have generally been prepared via the intermediacy of the 5,7-dihydroxy compounds. For example, the dihydroxy compounds can be halogenated to the 5,7-dihalo analogs, which in turn can be reacted with alkoxides to provide the corresponding 5,7-dialkoxy compounds. ##STR2##
The 5,7-dihydroxy compounds have been disclosed as being prepared by the cyclization of N-(3-(((aryl)amino)sulfonyl)-1H-1,2,4-triazol-5-yl)amines (II) with dialkyl malonates in the presence of sodium alkoxide in alcohol followed by acidification of the intermediate trisodium salt (III). ##STR3##
This process has the following disadvantages:
(1) the reaction time for the cyclization is generally 24 to 48 hours (hr); PA0 (2) the process requires 3 equivalents of expensive sodium alkoxide base; PA0 (3) on acidification, the intermediate trisodium salt (III) yields approximately 5 to 25 percent ring-opened product (V) which can be lost during the isolation of the desired product (IV); and PA0 (4) the neutralization process requires 3 equivalents of acid and generates considerable quantities of waste brine. PA0 Y represents H, F, Cl, Br, CF.sub.3 or NO.sub.2, PA0 R represents H, lower alkyl or lower alkoxy, and PA0 Z represents H, Cl or Br,
In view of the valuable herbicidal properties of the sulfonamides (I), it is desirable to have a process for the preparation of N-(aryl)-5,7-dihydroxy-1,2,4-triazolo[1,5-a]pyrimidine-2-sulfonamides which avoids unnecessary yield loss. It is also desirable to have a process that eliminates the sodium alkoxide base, does not generate large amounts of waste brine, and does not require protracted reaction times.